Improvement of breast cancer irradiation techniques

In this thesis a number of improvements of breast cancer radiotherapy techniques are described, resulting in a reduction of cardiac mortality. Target volume localization, patient positioning, and treatment planning studies were performed. The accuracy of localization of the internal mammary lymph nodes, using sonography, lymphoscintigraphy, and computer-tomograpy, as well as the inter-and intraobserver variations in the delineation of the breast CTV on CT-scans, are quantified. The amount of heart and lung inside tangential treatment fields is quantified for patients lying supine with both arms in a forearm support and with the ipsilateral arm positioned using an “L-bar.” Conventional rectangular tangential field irradiation is compared with newly developed conformal and IMRT tangential field irradiation techniques for irradiation of the left breast. For the combined treatment of the internal mammary lymph nodes and left-sided breast the wide split tangent technique is compared with two new techniques: a tangential field IMRT technique and a technique using oblique electron-photon fields to irradiate the lymph nodes combined with tangential fields to irradiate the breast. The CT-based conformal and IMRT treatment techniques lead to better sparing of the heart. However, these techniques are at this moment more time consuming than conventional, simulator-based treatments. Therefore, a patient selection criterion was developed using the maximum heart distance (MHD) as can be seen on a beam's eye view of a medio-lateral tangential field. It was shown that the MHD is a good estimator for the probability of late cardiac mortality and can be used to select patients that should be treated with a conformal or IMRT treatment technique.